Black oil conversion process startup procedure

ABSTRACT

A startup method for a process designed to effect the conversion of hydrocarbonaceous black oils. Applicable to a fixed-bed catalytic system, the method involves (1) prewetting the catalyst with a hydrocarbon mixture and (2) low-temperature reduction and sulfiding using circulating (recycle) hydrogen and a sulfurous hydrocarbon mixture.

United States Patent Nagl ' 73} Assignee:

[54] BLACK OIL CONVERSION PROCESS STARTUP PROCEDURE [72] Inventor: Gary J. Nagl, Downers Grove, Ill.

Universal Oil Products Company, Des Plaines, ill,

22 Filed: June 19, 1970 21 Appl.No.: 47,905

[ Feb. 15, 1972 3,423,307 1/1969 McKinney et al ......208/2l6 3 ,441,500 4/1969 Wunderlich ....208/2 1 6 3,528,910 9/1970 Haney et al ..208/216 Primary Examiner-Delbert E. Gantz Assistant Examiner-G. J. Crasanakis Attorney.lames R. Hoatson, Jr. and Robert W. Erickson ABSTRACT A startup method for a process designed to effect-the conversion of hydrocarbonaceous black oils. Applicable to a fixedbed catalytic system, the method involves (l) prewetting the catalyst with a hydrocarbon mixture and (2) low-temperature reduction and sulfiding using circulating (recycle) hydrogen and a sulfurous-hydrocarbon mixture.

3 Claims, No Drawings BLACK on. CONVERSION PROCESS STARTUP PROCEDURE APPLICABILITY OF INVENTION The present invention is applicable for use in a catalytic process for the conversion of hydrocarbonaceous black oils. More specifically, the inventive concept described herein is directed toward a procedure for placing such a process onstream. In essence, therefore, my invention provides a startup method for a catalytic black oil conversion process. As utilized herein, the term conversion is intended to encompass desulfurization, denitrification, hydrocracking, hydrogenation, etc., all of which reactions are effected in a black oil conversion process.

Certain fractions (distillates) of full boiling range crude oils, particularly the heavy oils extracted from tar sands, atmospheric and vacuum tower bottoms products, coal oils, etc., contain large concentrations of relatively high molecular weight sulfurous and nitrogenous compounds. In addition, these hydrocarbonaceous mixtures contain organometallic complexes, principally comprising nickel and vanadium, and asphaltenic compounds, the latter generally found to be complexed with sulfur. An abundant supply of such material exists, and virtually demands conversion for the purpose of satisfying the ever-increasing need for greater quantities of lower-boiling products.

In general, black oils are categorized in the art as heavy hydrocarbonaceous mixtures of which at least about 10.0 percent by volume boils above a temperature of about 1050 F. Furthermore, the vast majority of black oils have a gravity less than about 20.0 A.P.l., and often below about 10.0 A.P.l. Exemplary of those black oil charge stocks, to the conversion of which the present invention is adaptable, are a vacuum tower bottoms product having a gravity of 7.1 A.P.I., and containing 23.7 percent by weight of asphaltics and 4.1 percent by weight of sulfur; a topped Middle-East Kuwait crude oil having a gravity of 11.0 A.P.l., and containing 10.1 percent by weight of asphaltics and 5.2 percent by weight of sulfur; and, a vacuum residuum containing about 3.0 percent by weight of sulfur and more than 4,000 ppm of nitrogen, and having a 20.0 percent volumetric distillation temperature of about l,055 F. Principal difficulties accompanying the conversion of such hydrocarbonaceous black oils arise primarily from the presence of the asphaltic material. The asphaltenes are nondistillable coke precursors, insoluble in light hydrocarbons such as propane, pentane and heptane, and severely adversely affect the stability of the selected catalytic composite utilized in the conversion zone. The sue of the startup procedure of the present invention increases the stability of the catalyst when processing such hydrocarbonaceous black oils.

OBJECTS AND EMBODIMENTS A principal object of my invention is to improve processes designed to effect the conversion of sulfurous black oil charge stocks.

Another object is to provide a startup method for a catalytic black oil conversion process. A corollary objective is to enhance catalyst stability when processing hydrocarbonaceous black oils.

Therefore, in one embodiment, my invention affords a startup procedure for a catalytic black oil desulfurization process which comprises the steps of (a) circulating substantially pure hydrogen through a reaction zone containing a fixedbed of desulfurization catalyst while raising the pressure to a level within the range of about 1,000 to about 5,000 p.s.i.g. and increasing the temperature to a level of about 200 to about 400 F.; (b) continuing the hydrogen circulation at said temperature and pressure, and introducing a hydrocarbon mixture, containing sulfurous compounds, at a liquid hourly space velocity in the range of about 0.5 to about 1.5; (c) increasing the temperature to a level in the range of 400 to about 500 F.; (d) continuing the circulation of said hydrocarbon mixture and hydrogen until said circulating hydrogen attains an equilibrium concentration of hydrogen sulfide; and, (e) introducing said black oil while increasing said temperature to a level of from 700 to about 900 F.

Other objects and embodiments involve the type of sulfurous hydrocarbon mixture employed to presulfide the catalyst at the low temperature of 400 to about 500 F., various catalytic composites which experience increased stability,

operating conditions and techniques, etc. These, as well as other objects and embodiments, will become evident from the following additional description of the present invention.

SUMMARY OF INVENTION Recognition must be made of the many black oil conversion processes described in the literature, including U.S. patents. Typical processes and techniques are described in the following: U.S. Pat. No. 3,501,396 (Cl. 208-216); U.S. Pat. No. 3,471,397 (Cl. 208-111); U.S. Pat. No. 3,445,377 (Cl. 208-93); U.S. Pat. No. 3,429,801 (Cl. 208-58); U.S. Pat. No. 3,409,538 (Cl. 208-59); U.S. Pat. No. 3,375,189 (Cl. 208-59); and, U.S. Pat. No. 3,371,029 (Cl. 208-102). The processes, as well as many other employing a fixed-bed catalytic reaction zone, are those which can be improved through the use of my invention.

One common aspect of the black oil conversion processes resides in the use of catalytic composites containing at least one metallic component from Groups Vl-B and VIII, combined with a porous carrier material which may be either amorphous, or zeolitic in nature. Thus, according to the Periodic Table of Elements, E. H. Sargent & Company, 1964, the catalyst will comprise one or more metals from the group of tungsten, molybdenum, chromium, iron, cobalt, nickel, iridium, osmium, ruthenium, rhodium, platinum and palladium. The porous carriermaterial generally is a composite of alumina and silica with the latter being in a concentration of 10.0 to about 90.0 percent by weight.

Regardless of the precise composition of these black oil conversion catalysts, or the method by which they are prepared, it is generally conceded that they must be reduced and sulfided. The present invention is founded upon recognition of a method for reducing and sulfiding the catalytic composite; this method is incorporated as an integral part of a startup procedure. In the past, catalysts have been reduced and sulfided during the course of the manufacturing procedure with a mixture of hydrogen and hydrogen sulfide at tempera-. tures ranging from 500 to about 900 F. Another method involves reduction and sulfiding in situ utilizing the fresh feed sulfurous charge stock or another, different hydrocarbon mixture also containing sulfurous 'compounds. In the latter method, the technique is efi'ected at reaction conditions including a temperature in the range of 700 to about 900 F. Unless otherwise specifically'set forth, a statement regarding temperature, in the present specification and appended claims, alludes to the maximum catalyst bed temperature within the conversion reaction zone. In addition to a temperature in the range of 700 to about 900 F., black oil conversion conditions include a pressure from 1,000 to about 5,000 p.s.i.g. a hydrogen concentration from 5,000 s.c.f./bbl. and a liquid hourly space velocity (defined as volumes of fresh feed liquid charge per hour, measured at 60 F., per volume of catalyst disposed within the reaction zone) in the range of about 0.2 to about 3.0. Since the bulk of reactions are exothermic in nature, an increasing temperature gradient will be experienced as the hydrogen and charge stock traverse the catalyst bed. Preservation of the catalytic composite is effected by controlling the maximum catalyst bed temperature below about 900 F. The prior art processes recognize the advisability of utilizing liquid and/or gaseous quench streams, introduced at one or more intermediate loci, tovcontrol the maximum catalyst bed temperature in the aforesaid range. The foregoing represents the type of black oil conversion process to which the startup procedure herein described affords improvement.

In further describing my invention, it will be presumed that the catalytic composite has not been reduced and presulfided during the manufacturing procedure. In accordance with prior art techniques reduction and sulfiding of the catalyst has been effected at reaction conditions using a recirculating hydrogen stream containing hydrogen sulfide. More recently, the prior art has indicated a preference for utilizing a sulfurous hydrocarbon mixture, which may be the black oil intended for conversion, at temperatures somewhat below those to be employed in the process itself. Thus, after the system has been dried, using circulating hydrogen, or some inert gas such as nitrogen or air, hydrogen is circulated while the temperature is being increased to a level of from about 550 up to about 700 F. The sulfurous hydrocarbon mixturei.e., a vacuum gas oil free from nondistillables-is introduced, and processed in admixture with the circulating hydrogen. The reactor effluent is separated to provide a liquid phase and a hydrogen-rich vapor phase. The latter is monitored with respect to hydrogen sulfide concentration which increases as the catalytic composite becomes sulfided. When the concentration attains an equilibrium level, the black oil feed is introduced,'the temperature increased to the desired operating level and the flow of the sulfurous hydrocarbon mixture is ceased.

in accordance with my invention, the startup technique proceeds along similar lines, with several notable and essential differences. Substantially pure hydrogen is circulated while the pressure is increased to the operational level in the range of 1,000 to about 5,000 p.s.i.g.--i.e., about 2,000 p.s.i.g.-and the temperature is increased to a level of about 200 to about 400 F.-i.e., about 300 F. Hydrogen circulation is continued at these conditions while a sulfurous hydrocarbon mixture is introduced at a liquid hourly space velocity less than about 1.5, with a lower limit of about 0.5, in order to prewet the catalyst prior to effecting the presulfiding. Although the black oil charge stock may be used for this purpose it appears that better results are obtainable when a different hydrocarbon mixture is employed, and preferably one which is free from nondistillable hydrocarbons-Le, a catalytically cracked light cycle oil. Prewetting of the catalyst in this manner facilitates liquid distribution throughout the reaction zone during the presulfiding technique and black oil conversion. The prewetting may be accomplished by: (a) flooding the reaction zone by pumping the sulfurous hydrocarbon mixture upflow until all gaseous components are displaced; (2) pumping down flow until all gaseous components are removed via solution losses; and, (3) charging the lighter hydrocarbon mixture for an extended period of from 2 to about 24 hours; the latter technique is preferred.

After the catalyst has been thoroughly prewetted, the temperature is increased to a level in the range of 400 to about 500 F. for the sulfiding operation. As in the prior art procedures, the hydrogen sulfide concentration in the hydrogen-rich gaseous phase is monitored to determine the time when an equilibrium content is attained. At this stage, the black oil charge stock is introduced, the flow of sulfiding oil is ceased and the temperature increased to the operational level in the range of 700 to about 900 F. In a slightly different embodiment, the flow of the sulfiding oil is continued while the temperature is increased to 500 to about 600 F., at which time the black oil is introduced, and the temperature further increased as aforesaid.

ILLUSTRATlVE EMBODIMENT This illustrative embodiment is presented by way of an example in which a comparison is made between the present technique and the prior art procedure wherein the reduction and presulfiding takes place at temperatures above 500 F. The black oil charge stock was a reduced crude oil having the properties indicated in the following Table I:

TABLE 1: Reduced Crudc Properties Gravity, A.P.l. 17.0 100 ml. Distillation, F.

initial Boiling Point 550 500% R70 70.0% 1,030 End Boiling Point 1,040 Sulfur, wt.% 4.04 Nitrogen, p.p1m. 2.030 Heptane-insolubles, wt.% 2.38 Metals, p.p.m.

73.0% by volume distillablc at [,040 F.

The catalyst employed was a composite of 2.0 percent by weight of cobalt and 16.0 percent by weight of molybdenum, calculated as the elemental metals, combined with an aluminasilica carrier material containing 12.0 percent by weight of silica. This catalyst was not reduced or presulfided during the course of its manufacturing procedure. In a first operation, hereinafter referred to as Run 1, the catalyst was prewetted at a temperature of 300 F. and a liquid hourly space velocity of 2.0, by flooding the conversion zone upflow. The sulfurous hydrocarbon mixture employed in the prewetting technique was a light cycle oil having the properties shown in the following Table 11:

TABLE I1: Llght Cycle Oil Properties Gravity, A.P.1. 22.6

ml. Distillation. F.

Initial Boiling Point 415 50% 445 10.0% 45X 90.0% 603 End Boiling Point 671 Nitrogen, p.p.m. 200

Following the prewetting technique, the temperature was raised to a level of 550 F., with the pressure at 2,000 p.s.i.g. and the hydrogen concentration at 5,000 s.c.f/bbl. After a period of about 14 hours, the hydrogen sulfide concentration of the gaseous phase from the product effluent attained an equilibrium level of about 900 grains/100 s.c.f. At this point the reduced crude charge stock was introduced, at a liquid hourly space velocity of 0.8, and the flow of the light cycle oil sulfiding medium was ceased. The pressure was maintained at 2,000 p.s.i.g. and the hydrogen circulation at about 5,000 s.c.f./bbl. Temperature changes were made periodically in order to maintain the sulfur content of the normally liquid product at 1.0 percent by weight.

A second operation, hereinafter referred to as Run 11, was effected using a different portion of the same cobalt/molybdenum catalyst. Prewetting of the catalyst was effected with the light cycle oil at a pressure of 2,000 p.s.i.g., a temperature of 300 F., a liquid hourly space velocity of0.8 and with circulating hydrogen in an amount of 5,000 s.c.f./bbl. Following a period of 18 hours, during which prewetting was completed, the temperature was increased to a level of only 450 F., all other conditions remaining unchanged. After a period of about 32 hours, the hydrogen sulfide concentration of the gaseous phase attained an equilibrium level of 750 grains/100 s.c.f. The reduced crude was introduced and the flow of light cycle oil was ceased. Again the temperature was changed periodically to maintain the normally liquid product sulfur level at 1.0 percent by weight. The other conditions remained unchanged.

ln the following Table III, the operating temperature, required to maintain the 1.0 sulfur level, is correlated with catalyst life increments for both Run 1 and Run 1]. Catalyst life is conveniently expressed as barrels of charge stock processed per pound of catalyst disposed within the reaction zone.

TABLE 111: Catalyst Stabi lity Comparison Catalyst Life, bhL/lh. Temperature. F.

Considering the catalyst life period from 1.6 to 4.0 bbl./lb., the prior art presulfiding procedure resulted in a catalyst which required a 25 F. temperature increase over the 2.4 incremental bbl./lb. of catalyst life, while the catalyst presulfided according to my invention required only a F. temperature increase over the same period. In terms of F./bbl./lb., the stability factor from my startup procedure was 2.1, whereas that from the prior art technique was 10.4.

The foregoing specification and example illustrate the startup technique of the present invention and the benefits to be afforded through the utilization thereof.

I claim as my invention:

1. A startup procedure for a catalytic black oil desulfurization process which comprises the steps of:

a. circulating substantially pure hydrogen through a reaction zone containing a fixed-bed of desulfurization catalyst while raising the pressure to a level within the range of about 1,000 to about 5,000 p.s.i.g. and increasing the temperature to a level of 200 to about 400 F.;

b. continuing the hydrogen circulation at said temperatureand pressure, and introducing a hydrocarbon mixture, containing sulfurous compounds to preset said catalyst, at a liquid hourly space velocity in the range of about 0.5 to about 1.5;

c. increasing the temperature to a level in the range of 400 to about 500 F. to said catalyst;

d. continuing the circulation of said hydrocarbon mixture and hydrogen until said circulating hydrogen attains an equilibrium concentration of hydrogen sulfide; and,

e. introducing said black oil while increasing said temperature to a level of from 700 to about 900 F.

2. The method of claim 1 further characterized in that said hydrocarbon mixture is said black oil.

3. The method of claim 1 further characterized in that said hydrocarbon mixture is different from said black oil and the flow of said hydrocarbon mixture is ceased while said black oil is introduced. 

2. The method of claim 1 further characterized in that said hydrocarbon mixture is said black oil.
 3. The method of claim 1 further characterized in that said hydrocarbon mixture is different from said black oil and the flow of said hydrocarbon mixture is ceased while said black oil is introduced. 